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2009年  第16卷  第3期

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Minerals
Flotation of niobite,fersmite,and ilmenorutile
Hao Ren, Gui-lan Song, Fei-fei Ji
2009, 16(3): 249-254. doi: 10.1016/S1674-4799(09)00003-X
摘要:
The flotation ofniobite, fersmite, and ilmenorutile was studied using 3 collectors with various concentration and pulp pH. The collecting property of different representative collectors was investigated. Experimental results show that diphosphonic acid is an effective collector for valuable niobium-containing minerals. A flotation recovery of 90.87%-91.7% is obtained with 75 mg/L diphosphonic acid at pH 2-4. The chemical adsorption of diphosphonic acid on these 3 minerals' surface might lead to the high recovery efficiency of the minerals, which is proved by IR and X-ray photoelectron spectroscopy spectra.
Minerals
Simulation experiment of AE-based localization damage and deformation characteristic on covering rock in mined-out area
Sheng-jun Miao, Xing-ping Lai, Xing-guang Zhao, Fen-hua Ren
2009, 16(3): 255-260. doi: 10.1016/S1674-4799(09)60046-7
摘要:
The localization damage and deformation characteristics of multiple rock in mined-out area under thick soil layer were investigated by acoustic emission (AE)-based physical similar simulation experiment and damage test combined with the AE theory on rock damage. During different mining courses, the degree of wall rock suffered from mining disturbed process in mined-out area was different, so did the AE density of initial damage and fracture. Some characteristic parameters, including large events, total events, and energy rate, presented fluctuations with temporal and spatial change and take on a certain extent statistic relation. Subsequently, the percent of damage degree was defined and divided into 4 stages, and the localization damage and deformation characteristics of surrounding rock in mined-out area and coal pillars were analyzed quantitatively.
Metallurgy
Solidification and crystallization properties of CaO-SiO2-Na2O based mold fluxes
Sheng-ping He, K. C. Mills
2009, 16(3): 261-264. doi: 10.1016/S1674-4799(09)60047-9
摘要:
Crystallization properties play an important role in keeping a smooth running of continuous casting process and high surface quality of cast strands. To reduce fluorine pollution in slag, a new type of CaO-SiO2-Na2O (CSN) based mold flux was studied. The solidification and crystallization properties, including crystallization temperature, crystallization ratio and solidification mineragraphy, were measured, which were compared with the CaO-SiO2-CaF2 (GF) mold flux. The results show that the crystallization performance is equal to the high fluoride mold powder and CSN can be used for peritectic steel grades sensitive to longitudinal cracking in continuous casting.
Metallurgy
Effect of sinter layer porosity distribution on flow and temperature fields in a sinter cooler
Jik-chang Leong, Kai-wun Jin, Jia-shyan Shiau, Tzer-ming Jeng, Chang-hsien Tai
2009, 16(3): 265-272. doi: 10.1016/S1674-4799(09)60048-0
摘要:
When sinters are filled into the sinter cooler from the sintering machine, it is commonly seen that, due to segregation effects, sinters of larger size usually accumulate closer to the inner wall of the sinter cooler, whereas those of smaller size are to the outer wall. This nonuniform distribution of sinters has led to uneven cooling effect throughout the cooler. This causes the sinters leaving the cooler at a large temperature difference. This undesired temperature difference leads to the deformation and even the destruction of the conveyors. The computational fluid dynamics (CFD) technique was used in the present work to investigate the heat and fluid flow phenomena within the sinter cooler corresponding to the different distribution of sinter layer porosity, which was highly dependent on the arrangement and orientation of sinters within the sinter cooler. It is confirmed that a high mass flow rate within the sinter layer causes a low temperature region and vice versa. The flow fields for vertically reducing porosity distribution and random distribution are almost identical indicating the relative insignificance of convective heat transfer mechanism.
Metallurgy
Experimental study on 830 MPa grade pipeline steel containing chromium
Yi Ren, Shuai Zhang, Shuang Wang, Wen-yue Liu
2009, 16(3): 273-277. doi: 10.1016/S1674-4799(09)60049-2
摘要:
The diversity of microstructure and properties of 830 MPa grade pipeline steel containing chromium was investigated by optical microscope and transmission electron microscopy. The main microstructures were multiple configurations, containing lath bainite and granule bainitc. Mechanical properties test results showed that the yield strength and tensile strength improved with increasing chromium content. The toughness and elongation decreased at the same time, so temper process was introduced. Appling proper temper parameters, the values of toughness and elongation were improved dramatically, and the strength decreased slightly.
Metallurgy
Reaction zone characterization of counter-flow diffusion flame with diluted and preheated reactants
Yu-ying Liu, Jean-michel Most, Philipp Bauer, Alain Claverie
2009, 16(3): 278-284. doi: 10.1016/S1674-4799(09)60050-9
摘要:
Reaction zone characteristics were studied using hydroxy radical planar laser-induced fluorescence (OH-PLIF) technique for a counter-flow preheated (CH4+N2)/(Air+N2) diluted diffusion flames. The effects of preheat temperature and dilute ratio on the reaction zone characteristics were investigated by demonstrating the OH intensity distribution and reaction zone thickness from OH-PLIF images. Under the experimental conditions of constant cold flow velocity, the results show that the OH intensity and reaction zone thickness decrease with the increase of dilute ratio at constant preheat temperature and increase with preheat temperature at fixed dilute ratio. The OH maximum intensity shifts towards the "lean" side of counter flow at constant preheat temperature, and it shifts towards the fuel side with the increase of dilute ratio of fuel stream and towards the oxidizer side with the increase of dilute ratio of oxidizer stream respectively. The feasibility of OH as a reaction zone marker in this diluted combustion is verified further. The variation of diffusion and chemical reaction rate of reactants due to preheat and dilution contributes to the reaction zone characteristics simultaneously. The effect of strain on the flame reaction zone should be included in the future work.
Materials
Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure
Xue-xia Xu, Yang Yu, Wen-long Cui, Bing-zhe Bai, Jia-lin Gu
2009, 16(3): 285-292. doi: 10.1016/S1674-4799(09)60051-0
摘要:
The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite (CFB/M) complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a frequency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 107 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fatigue cycle exceeds 107, and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of "soft structure". It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fatigue mechanism was discussed and it is suggested that specific CFB/M complex microstructure of the studied steel contributes to its superior properties.
Materials
Antibacterial and corrosive properties of copper implanted austenitic stainless steel
Juan Xiong, Bo-fan Xu, Hong-wei Ni
2009, 16(3): 293-298. doi: 10.1016/S1674-4799(09)60052-2
摘要:
Copper ions were implanted into austenitic stainless steel (SS) by metal vapor vacuum arc with a energy of 100 keV and an ions dose range of (0.5-8.0)×1017 cm-2. The Cu-implanted SS was annealed in an Ar atmosphere furnace. Glancing X-ray diffraction (GXRD), transmission electron microscopy (TEM) and Auger electron spectroscopy (AES) were used to reveal the phase compositions, microstructures, and concentration profiles of copper ions in the implanted layer. The results show that the antibacterial property of Cu-implanted SS is attributed to Cu9.9Fe0.1, which precipitated as needles. The depth of copper in Cu-implanted SS with annealing treatment is greater than that in Cu-implanted SS without annealing treatment, which improves the antibacterial property against S. aureus. The salt wetting-drying combined cyclic test was used to evaluate the corrosion-resistance of antibacterial SS, and the results reveal that the antibacterial SS has a level of corrosion-resistance equivalent to that of un-implanted SS.
Materials
Evolution of carbides and carbon content in matrix of an ultra-high carbon sintered steel during heat treatment process
Yuan-zhi Zhu, Zhe Zhu, Zhi-min Yin, Zhi-dong Xiang
2009, 16(3): 299-303. doi: 10.1016/S1674-4799(09)60053-4
摘要:
DTA, thermal expansion, XRD, and SEM were used to evaluate the effect of quenching temperature on the mechanical properties and microstructure of a novel sintered steel Fe-6Co-1Ni-5Cr-5Mo-1C. Lattice parameters and the mass fraction of carbon dissolved in the matrix of the steel quenched were investigated. It is discovered that the hardness of the steel increases with quenching temperature in the range of 840-900℃ and remains constant in the range of 900 to 1100℃. It decreases rapidly when the temperature is higher than 1100℃. The mass fraction of carbon dissolved in the matrix of the steel quenched at 840℃ is 0.38, but when the quenching temperature is increased to 1150℃, it increases to 0.98. The carbides formed during sintering are still present at grain boundaries and in the matrix of the steel quenched at low quenching temperatures, such as 840℃. When the quenching temperature is increased to 1150℃, most of the carbides at grain boundaries are dissolved with just a small amount of spherical M23C6 existing in the matrix of the quenched steel.
Materials
Numerical simulation of the temperature fields of stainless steel with different roller parameters during twin-roll strip casting
Yuan Fang, Zhen-min Wang, Qing-xiang Yang, Yun-kun Zhang, Li-gang Liu, Hong-yan Hu, Yue Zhang
2009, 16(3): 304-308. doi: 10.1016/S1674-4799(09)60054-6
摘要:
The temperature field of stainless steel during twin-roll strip casting was simulated by experiment and a finite element (FE) model. By comparing the measured result with the simulated values, it is found that they fit close to each other, which indicates this FE model is effective. Based on this model, the effects of roll gap (t) and roll radius (R) on solidification were simulated. The simulated results give the relationship between t or R and the position of the freezing point. The larger the t is and the smaller the R is, the closer the position of the freezing point is to the exit.
Materials
Investigation on inductive heating of A356 alloy for thixo-forming
Kai-kun Wang, Jian-lin Sun, Yong-lin Kang, Qi Zhang, Lei Yang, Chun-mei Ma
2009, 16(3): 309-313. doi: 10.1016/S1674-4799(09)60055-8
摘要:
To meet the demands of continuous stream-line for component production in the thixo-forming industry, billet heating should be of high quality and in a controllable way. A 4-step inductive heating strategy for aluminum alloy A356 was performed. Thixotropic testing and microstructure analysis showed that a homogenous temperature distribution was achieved after temperature-power-time optimization. Theoretical analysis was given concerning the thermal conductivity and heat capacity of A356 between conventional and semisolid casting microstructures. The experimental results show that the optimized 4-step strategy could be the best strategy for billet heating during the thixo-forming of aluminum alloy A356.
Materials
Magnetic properties of Fe3(1-x)Cr3xC alloys
Feng-Qi Zhao, O. Tegus, B. Fuquan, E. Brück
2009, 16(3): 314-316. doi: 10.1016/S1674-4799(09)60056-X
摘要:
The magnetic properties of Fe3(1-x)Cr3xC alloys with x=0.05, 0.1, 0.15, and 0.2, which crystallize in the cementite Fe3C-type structure with space group Pnma, were investigated by means of magnetization measurements. These alloys show temperature-induced second-order magnetic phase transitions. The Curie temperature (Tc) of these alloys decreases with increasing x. The isothermal magnetic-entropy changes of these alloys were derived from the magnetic isotherms measured with increasing temperature and increasing field. The maximum values of the magnetic-entropy change are about 0.9 and 3.6 J·kg-1·K-1 at Tc=360 K for x = 0.05 in a magnetic field change from 0 to 1 T and 0 to 5 T, respectively.
Materials
Effect of Fe metal on the growth of silicon oxide nanowires
Wei-long Liu, Shu-huei Hsieh, Ching He Chen, Wen-jauh Chen
2009, 16(3): 317-321. doi: 10.1016/S1674-4799(09)60057-1
摘要:
Silicon oxide (SiOx) nanowires are generally grown on Si substrate under the catalysis of Au in N2 atmosphere at elevated temperatures. Because the price of Au metal is quite high, Fe metal is then used to replace a part of Au for catalyzing the growth of SiOx nanowires. The results show that the Fe film can be used as the diffusion barrier of Au. SiOx nanowires are grown on Au/Fe/Si substrate at 1030℃. Under the catalysis of Fe/Au, the efficiency for the growth of SiOx nanowires is promoted.
Materials
Preparation of β-SiC by combustion synthesis in a large-scale reactor
Yu-qiong Liu, Li-feng Zhang, Qing-zhi Yan, Xiao-dong Mao, Qiao Feng, Chang-chun Ge
2009, 16(3): 322-326. doi: 10.1016/S1674-4799(09)60058-3
摘要:
The feasibility of 5 kg β-SiC synthesized in one batch was demonstrated through igniting the mixture of Si, C-black and polytetrafluoroethylene (PTFE) under different nitrogen pressures. The effect of experimental parameters, including the contents of PTFE, nitrogen pressure, preheating, and raw materials distribution forms were investigated. The results show that the products are β-SiC with equiaxed grains. The average grain size is less than 200 nm. The powders loaded loosely promote reaction heat dispersing, resulting in small grains. High purity β-SiC powders are obtained when the PTFE content is as low as 5wt%, which simplifies the process and decreases the cost effectively. The ceramic sintered from the obtained β-SiC powders presents the hardness of 22.20 GPa, the bending strength as high as 715.15 MPa and the fracture toughness of 8.179 MPa·m1/2, which are higher than those of ceramics fabricated with α-SiC produced by combustion synthesis.
Materials
Wettability and pressureless infiltration mechanism in SiC-Cu systems
Lin Zhang, Xuan-hui Qu, Bai-hua Duan, Xin-bo He, Ming-li Qin, Shu-bin Ren
2009, 16(3): 327-333. doi: 10.1016/S1674-4799(09)60059-5
摘要:
The wetting behavior of copper alloys on SiC substrates was studied by a sessile drop technique. The microstructure of SiCp/Cu composites and the pressureless infiltration mechanism were analyzed. The results indicate that Ti and Cr are effective elements to improve the wettability, while Ni, Fe, and Al have minor influence on the improvement of wettability. Non-wetting to wetting transition occurs at 1210 and 1190℃ for Cu-3Al-3Ni-9Si and Cu-3Si-2Al-1Ti, respectively. All the copper alloys react with SiC at the interface forming a reaction layer except for Cu-3Al-3Ni-9Si. High Si content favors the suppression of interracial reaction. The infiltration mechanism during pressureless infiltration is attributed to the decomposition of SiC. The beneficial effect of Fe, Ni, and Al is to favor the dissolution of SiC. The real active element during pressureless infiltration is Si.
Materials
Microstructure and properties of SiC gradiently coated Cf/C composites prepared by a RCLD method
Jun-hua Chen, Guang-li Chen, Hao-ran Geng, Yan Wang
2009, 16(3): 334-338. doi: 10.1016/S1674-4799(09)60060-1
摘要:
The SiC gradiently coated carbon fiber/carbon (Cf/C) composites were prepared by a two-step rapid chemical liquid deposition (RCLD) method. The microstructure and properties of the composites were investigated using X-ray diffraction, scanning electron microscopy together with energy dispersive X-ray analysis, bending tests, and oxidation tests. The experimental results show that the surface layer of the composites is composed of SiC, pyrocarbon, and carbon fibers. Their inner area consists of pyrocarbon and carbon fibers. The SiC content gradiently decreases with increasing distance from the outer surface to the center of the composites. Furthermore, the thickness of the SiC layer increases with increasing tetraethylorthosilicate content and deposition time. SiC coatings have no significant influence on the bending strength of the composites. However, the oxidation resistance of the composites increases with increasing thickness of the SiC layer.
Materials
Oxidation behavior of in-situ Al2O3/TiAl composites at 900℃ in static air
Tao-tao Ai, Fen Wang, Xiao-ming Feng
2009, 16(3): 339-344. doi: 10.1016/S1674-4799(09)60061-3
摘要:
In-situ Al2O3/TiAl composites were successfully synthesized from the starting powders of Ti, Al, TiO2 and Nb2O5. The oxidation behavior of the composites at 900℃ in static air was investigated. The results indicate that the composite samples present a much lower oxidation mass gain. Under long-time intensive oxidation exposure, the formed oxide scale is multi-layer. The formation of the outer TiO2 layer is fine and dense, the internal Al2O3 scale has good adhesiveness with the outer TiO2 scale, and the TiO2+Al2O3 mixed layer forming the protective oxide scale is favorable for the improvement of oxidation resistance. It is believed that the incorporation of Al2O3 particulates into the metal matrix decreases the coefficient of thermal expansion of the substrate, and forms a local three-dimensional network structure that can hold the oxide scale. The formation of the oxide scale with finer particle size, stronger adherence, less micro-defects and slower growth rate can contribute to the improvement of oxidation resistance. Nb element plays an important role in reducing the internal oxidation action of the materials, restraining the growth of TiO2 crystals and promoting the stable formation of the Al2O3-riched layer, which is beneficial to improve the oxidation properties.
Materials
Effect of milling process on the core-shell structures and dielectric properties of fine-grained BaTiO3-based X7R ceramic materials
Tian Wang, Xiao-hui Wang, Hai Wen, Long-tu Li
2009, 16(3): 345-348. doi: 10.1016/S1674-4799(09)60062-5
摘要:
Fine-grained BaTiO3-based X7R ceramic materials were prepared and the effects of milling process on the core-shell structures and dielectric properties were investigated using scanning electron microscope, transmission electron microscope, and energy dispersive spectroscopy (EDS). As the milling time extends, the dielectric constant of the ceramics increases, whereas the temperature coefficient of capacitance at 125℃ drops quickly. The changes in dielectric properties are considered relevant to the microstructure evolution caused by the milling process. Defects on the surface of BaTiO3 particles increase because of the effects of milling process, which will make it easier for additives to diffuse into the interior grains. As the milling time increases, the shell region gets thicker and the core region gets smaller; however, EDS results show that the chemical inhomogeneity between grain core and grain shell becomes weaker.
Materials
Magnetic susceptibility measurements on metakaolin admixtured cement hydrated with ground water and sea water
D. Govindarajan, R. Gopalakrishnan
2009, 16(3): 349-354. doi: 10.1016/S1674-4799(09)60063-7
摘要:
The role of metakaolin in the properties of Portland cement hydrated with ground water and sea water was described by magnetic susceptibility study. Cement pastes containing 0wt%, 10wt%, 20wt% and 30wt% replacement of metakaolin and in a water/cement (W/C) ratio of 0.4 were prepared. The susceptibility at different hydration periods was determined by Faraday Curie balance and it was related to the changes in setting time and compressive strength of admixtured cement. Compared with sea water-treated cement paste, the magnetic susceptibility of ground water-treated cement paste is higher in value. The observed result shows that, irrespective of water, the magnetic susceptibility increases with increasing metakaolin percentage replacement level in cement.
Materials
Iron ore tailings used for the preparation of cementitious material by compound thermal activation
Zhong-lai Yi, Heng-hu Sun, Xiu-quan Wei, Chao Li
2009, 16(3): 355-358. doi: 10.1016/S1674-4799(09)60064-9
摘要:
In the background of little reuse and large stockpile for iron ore tailings, iron ore tailing from Chinese Tonghua were used as raw material to prepare cementitious materials. Cementitious properties of the iron ore tailings activated by compound thermal activation were studied. Testing methods, such as XRD, TG-DTA, and IR were used for researching the phase and structure variety of the iron ore railings in the process of compound thermal activation. The results reveal that a new cementitious material that contains 30wt% of the iron ore tailings can be obtained by compounded thermal activation, whose mortar strength can come up to the standard of 42.5 cement of China.